After his mom dies, and the landlord kicks him out, 12-year-old Jonathan faces the loneliness and danger of life on the streets — until he meets Lewis. Lewis takes him under his wing and leads him to his new home among a group of kids living in an abandoned underground shopping mall who call themselves the "Undergrounders." Now renamed "Mouse," Jonathan runs errands, delivers packages and panhandles for food money.

An escape from this life underground comes to him in the form of hockey gear. Stolen hockey gear, but hockey gear nonetheless. He suits up and heads to the community rink, where he befriends regular kids who welcome him into their game and onto their team. He agrees, knowing he can never tell them about being homeless.

Playing hockey makes him feel like a kid again, but keeping his double life a secret proves to be more difficult and dangerous than he ever could have imagined.